ruby: an introduction - who am i?

Ruby: An introduction - Who am I?

Maciej Mensfeld 1/23

Presented by:

Maciej Mensfeld

Ruby: An introduction

[email protected]

github.com/mensfeld

senior ruby [email protected] ruby [email protected]

Ruby: An introduction – please…


Please…

• …ask me to slow down, if I speak to quickly;• …ask me again, if I forget;

• …ask questions, if anything i say is not clear;• …feel free to share your own observations

Ruby: An introduction

Ruby: An introduction – What is Ruby?


Ruby WT*?

Ruby pictures

Ruby: An introduction – What is Ruby?


What is Ruby?

• Pure object-oriented programming language (even the number 1 is an instance of class);

• Created by Yukihiro Matsumoto in 1993;• Freely available and open-source;• Syntax is readable and easy to learn;• Being used for text processing, web apps, general system

administration, and AI and math research.• Can be extended with Ruby or low-level C;• Really helpful community;

Ruby: An introduction – What I love in Ruby?


Clarity not ceremony – Main program

Java:public class HelloWorld{ public static void main(String args){ System.out.println(„Hello World”); }}

Ruby:puts „Hello World”

Try it out!

Ruby: An introduction – What I love in Ruby?


Expressive syntax && objects, objects, objects…

3.times { puts „Ruby is cool”}[„Maciek”, „John”, „Anna”].first #=> „Maciek”[„Maciek”, „John”, „Anna”].last #=> „Anna”attr_accessor :name

„Anna”.class #=> Stringnil.class #=> NilClass1.class #=> Integer{}.class #=> Hash[].class #=> Arrayself.class #=> Object(0..9).class #=> Range

Ruby: An introduction – syntax


Ruby syntax – hello world as a function

Hello World! puts „Hello World!”def h puts „Hello World!”end

h => „Hello World!”

Hello YourName! puts „Hello #{name}”

def h(name=„World”) puts „Hello #{name}!”end

h („Maciek”)=> „Hello Maciek!”

Try it out!



Ruby syntax – classes, methods, objects

Hello YourName! as an object

# Comments starts with „#”class Messenger def initialize(name) # instance variables starts with „@” @name = name end

public def hello puts „Hello #{@name }!” endend

msg = Message.new(„Maciek”)msg.hello #=> „Hello Maciek!”

Try it out!



Ruby syntax – arrays, hashes (dictionaries)

Arrays names = [‘Maciek’, ‘John’, ‘Freddy’]

names.length #=> 3debts.length #=> 2

Hashes debts={„Maciek”=>1, „John”=> 10}



Ruby syntax – loops

Ruby:friends.each{|friend| puts friend }

C:for(i=0; i<number_of_elements;i++){ print element[i]}

10.times {|i| puts i }10.downto(1){|i| puts i }

There is no standard „for” loop in Ruby!

Try it out!



Ruby craziness - symbols

OMG symbols are so weird…

When you ask someone : what are symbols in Ruby? Most programmers will say: they simple are!

A symbol in Ruby is an instance of the class Symbol. A symbol is defined by prefixing a colon with an

identifier. :name, :id, :user

Symbols are most commonly used in creating hashes:h = {:name => "Jayson", :email => „[email protected]"}

The advantage in using symbols is the efficient use of memory. Maximum space taken by a symbol is never more than the space taken by an integer. This is because internally symbol is stored as an integer. In case of strings the memory space depends on the size of the string.



Ruby craziness - symbolsAlso whenever a string is used in the program, a new instance is created. But for symbols, same identifier points to the same memory location!

puts "name".object_idputs "name".object_idputs :name.object_idputs :name.object_id

Compare:puts "name".object_id == "name".object_idputs :name.object_id == :name.object_id

Try it out!

Ruby: writing some cool stuff

Maciej Mensfeld 23

Web crawler!

Enough theory!Let’s be pragmatic!

Simple web crawlerrequirements

Fetch and store urls

Don’t revisit urls

Search 4 keywords (support regexp)

Print results


Maciej Mensfeld 23

Web crawler – page content parser

What do we need?

Parser Crawler

Extracts data from page content Crawl all available pages


Maciej Mensfeld 23

Simple parser – 13LOC

attr_reader – set instance variable as readonly from the outsideattr_accessor – make instanca variable R/W from the outside




@keyword.is_a?(String) ? @keyword.downcase : @keyword

Just like in C and PHP:

condition_true ? if true do smthng : if false do smthng

Try it out! true ? puts(„I’m true!”) : puts(„I’m false!”)

false ? puts(„I’m true!”) : puts(„I’m false!”)




Try it out!



Crawler – How should it work?

Try to download page

Success?Select another

pageNo

Yes

Do something with result (parse, send, etc)

Mark page as visited



Crawler – 37LOC

Try it out!

Add our start url to a @new_urls array (basicly create @new_urls array with one address in it)

No pages where visited yet – so @visited_urls = [] (empty array)

We will check only pages with specified extensions (html, asp, php, etc)



Crawler – read page in Ruby

Try it out!

Mark page as visited (add it to @visited_urls array)Load current content page (parse URL and address)

Catch any type of exception (404, 500, etc) – mark page as visited so we don’t go there again and return false

Reading pages in Ruby is easy!



Crawler – extract URLs

Try it out!

Use URI.extract method to extract all urls from @current_contentCheck if URL is valid (try to parse it and check extension)

If anything failes – assume that this URL is incorrect

Reading pages in Ruby is easy!



Crawler – run crawler!

Try it out!



THX

Presented by:

Maciej Mensfeld

[email protected]

github.com/mensfeld

ruby: an introduction - who am i?

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